Centralized traffic controlling system for railroads



July 30, 1935.

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CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 5 Sheets-Sheet lFiled March 22, 1953 Y To ma@ BY MM @am /'Q/ ATroRNEY wr www? E BTS SCT,M L .z v 4 NL l ,wf ha :mmm| m|||L w. 1r. POWELL 2,009,946

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS july 30, 1935.

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Patented July 30, 1935 UNITED STATES CENTRALIZED TRAFFIC CONTROLLINGSYSTEM FOR RAILROADS Winfred T. Powell, Rochester, N. Y., assigner toGeneral Railway Signal Company,` Rochester,

Application March 22, 1933, Serial No. 662,116

20 Claims.

This invention relates to centralized traflic controlling systems forrailroads and it more particularly pertains to the communication part ofsuch systems.

The present invention contemplates a centralized traiilc controllingsystem in which communication is established between a control ofliceand a number of outlying iield stations by means of a communicationsystem of the selective coded duplex type. The switches and signals atthe outlying stations located along the railroad track are connected tothe control oice by means of a three-wire line circuit.

These switches and signals are under the supervision and control of anoperator at the control oiilce, so that he may at will change theposition of the switches subject to automatic approach and detectorlocking circuits which prevent unsafe operation of any switch. Theoperator may also at will hold at-stop any of the signals or allow themto clear, dependent upon the position of the associated switches andprovided the location of trains makes it safe for such signals toindicate proceed.

This system further provides means whereb-y indications are displayed inthe control oilice to provide the operator with the necessaryinformation for governing train movements, such as the indication of thepresence or absence of trains on the various track sections and thepositions and conditions of the various switches, signals and the like.

In this system a series of impulses forming a distinctive codecombination is transmitted over the l'me circuit for the selection of aparticular field station and for the transmission of controls to theselected station. Similarly, a series of impulses iorming a distinctivecode combination is transmitted over the line circuit for theregistration of a particular iield station in the control ofce and thetransmission of new indications from the registered station. The controland indication circuits are so interrelated with the selector typeapparatus employed that controls and/or indications are transmittedduring the same cycle of operations.

In the present invention, it is proposed to provide a line battery atthe control oce for energizing the line conductors to transmit controland indication impulses. The control impulses are made distinctive byreason of their polarity for the purpose of transmitting the codecombinations for selecting eld stations and for transmitting the desiredcontrols to the selected station. The indication combinations areformed, first by varying the time intervals or spaces between successiveimpulses applied to the line and second by arranging the return path forthe impulses by way of two of the three line conductors in particularsequence combinations, all of which will be more vspecifically pointedout in the detailed description.

As the system is of the coded duplex type, it is operable through cyclesof operation for the transmission of controls and/or for thetransmission of indications. When controls are transmitted, a particulariield station selecting code is iirst transmitted to select that stationwith which communication is desired, then this code is, followed by thecontrol impulses for transmitting controls to the selected station.Similarly,rwhen indications are transmitted, that particular rleld`station which istransmitting, rst transmits its.

station registering code and thereafter code combinations aretransmitted corresponding'to the indications which are to be transmittedfrom the registered station.

Irrespective of whether the control oice or a Ulf. 10

short (normal) or comparativelylong (abnorpulses for providing a portionof the'code com'-v binations, the iield station transmitting may pro--lvid-e the return path for the polar impulses which are applied to line Sat each step by way of the Aline conductor alone, the B lineconductor'alone or these two return lin-e conductors in'sequ'en'ce fcombinations for obtaining a choice of six code combinations per step.This choice of six combinations together with the choice of twocombinations obtained by means of the` short and long off periodsbetween impulses, makesiit possible to obtain a choice of twelvecombina'- tions per step.

-tion by way of example.

Certain ofthe characteristic features of this invention are disclosed inthe prior application of Neil D. Preston Ser. No. 644,481 led November26, 1932, and no claim is made herein to these features.

These characteristic features of the present invention will beeXplaine-d more in detail in the following description of oneembodimentof the invention and various other 'characteristic features, advantagesand functions will be in part pointed out and in part apparent as thedescription progresses.

In describing the invention in detail, reference will be made to theaccompanying drawings which illustrate one method of carrying out theinven- The drawings illustrate in a diagrammatic manner the apparatusand circuits employed and for convenience, those parts having similarfeatures and functions are designated in the several views by likeletter reference characters that are generally made distinctive veitherby reason` of distinctive exponents representative of their location orby reason of preceding numerals which represent the order of theiroperation and in Which:-

Fig. `lV diagrammatically illustrates the threewire-line circuitextending from the control ofiice through two intermediate fieldstations to the end fieldk station.

Figs; 2 and 3, when placed end to end in the order named, illustrate theapparatus and circuitsV employed at a typical control oice.

`Fig". 4 illustrates thel apparatus and circuits employed at a typicaleld station.

Fig.5 illustrates the wiring of the contacts of the'- four pilot relaysshown in Fig. 3.

Fig.' 6 illustrates a typical indication code table which'will -be'conveniently referred to when describing the method of `obtaining theindication combinations.

Forfth'epurpose of simplifying the illustrations land-facilitating inthe explanation, various parts and circuits have been showndiagrammaticallywith certain conventional illustrations employed andthe'drawings have been mad-e more with fthe purpose of making it easy tounderstand the-'principles and mode of operation of the invention,rather-than illustrating the specific constructionand arrangement ofparts that would be'lpreferably employed in practice.

The arrangement of those parts of the systemrwhichare' not illustratedin the drawings andrtheir cooperation an-dconnection with theillustrated portions will be set forth in the fol-- lowing. generaldescription. After the general description, amore detailed descriptionwill be given `offtlie operation-of the invention.

1 findicate .the positiveA and negative terminals respectiv-elyofsuitable batteries or other sources of `:direct current and the circuitswith which thesesymbolsrare used always have current owinginthesame-direction. The symbols (B-h) i and.(B-)..indicate connections tothe opposite terminalstof 'a-suitable battery or other directcurrentsource which has a central or intermediatetap'designated (CN andthe circuits with which these symbols are used may have current Y-flowing in. one-direction or the other depending upon the`particularterminal used in combination with.v the tap (CN).

ForI convenience in describing the operation of the=-system, the-'threeline` wires Aconnecting the control oiiice with the eld stations areidentified by referring to them as the stepping line (S) and the returnlines (A and B). At the control oiTlce, a line battery LB is arrangedtobe selectively connected in series with the stepping line conductorand the return line conductors for applying polar impulses to the lineduring outbound and duplex cycles. During an inbound cycle, line batteryLB is connected to the stepping line in the same manner for allimpulses, that is, a series of impulses is applied to line S.

The field station circuits illustrated in Fig. 4 have not been shown indetail. Only that portion of the field station circuits used during thetransmission of indications is shown in detail. The circuit organizationfor operating the stepping relays is the same as used in the controloffice, therefore, it is believed unnecessary to show the circuit wiringwhich controls these relays. The

. series of. dashes connecting the contacts of the line relay to thebracket associated with the stepping relay bank indicates that theserelays are controlled by the line relay at the station which operates insynchronism with the line relayin the control oiiice.

Similarly, the line repeating relay, the station relay and the slowacting relay at the eld station are connected by means of the series ofdashes to the contacts of the line relay which indicates that theserelays are also controlled over the line circuit. This control of thesevarious relays is completely disclosed in N. D. Preston application,Ser. No. 644,481, led November 26, 1932.

In Fig. 4, the three code jumper connections which determine the codecombination for the transmission of indications are shown in detail forthe first and second steps. It is believed that a complete explanationof the operation of this feature during the first `two steps will besuiiicient to indicate how these indication code combinations areobtained for as many steps as the size of the system requires.

In the upper portion of Fig. 6, the jumper wire connections and theresulting relay positions are indicated for the two distinctiveindications which are obtained duringthe first off period betweenimpulses in the line circuit. This portion of the code table indicatesthat the connection of a code jumper from wire 265 of Fig. 4 to resultsin a long off period and this in turn causes relays PLAl and PLBl to bepicked up, leaving relays PLTl and EPT down. Relay EPT down results inthe irst pilot relay PO (off) picking up. The alternate arrangement ofwire 205 of Fig.Y 4, that is disconnected from results in these variousrelays being in their alternate positions as indicated in this table.Therefore, the result of this selective jumper connection of wire 265 atthe station determines whether relay PO in the office will be up or downduring a particular step.

In the lower portion of Fig. 6, the six conditions are illustratedwhereby a choice of six indication code combinations per step isobtained. The pilot relays PF, IPB and ZPB which are to be conditionedas determined by the connections of the code jumpers to wires 206 and2U? at the eld station, are shown in the right hand portion ofthisillustration and it will be observed that these pilot relays are upand down in six different combinations, as indicated by referencecharacters U and D respectively.

Foi-convenience in describing the operation which results from thevarious connections of the sequence determining circuits, an "on periodsecond and third portions and the positions of the PLAl, PLBl, MA and MBrelays during these different yportions of an on period are indicated byreference characters D and U which indicate that an associated relay isdown or up respectively. 1 i

As will be clearly pointed out in the following description, the pickingup of relay PLA1 during an on period opens the Aline conductor, whichresults in relay MA remaining' down and the picking up of relay PLBlresults in opening line B so that relay MB remains down. In the table itwill be noticed that the reference character U occurs in associationwith the MA and MB relays during a particular portion of the on periodwhen the reference character D is associated with the corresponding PLA1and PLBl relays.

In order to pick up any of the three pilot relays, PF, IPB or 2PB, relayMB must be up. Pilot relay PF is picked up when relays MA and MB are upat the same time. Relay IPB is picked up when relay MA is down and relayMB is up before relay PF has been picked up. Relay ZPB is picked up whenrelay MA is down and relay MB is up after relay PF has been picked up.It will be noted that relay PF is up for the third, fourth, fifth andsixth combinations. This is because relays MA and MB are bothrup at thesame time only for th'ese four combinations and this occurs in thesecond portion of the on period.

The rst combination results in all three pilot relays remaining downbecause relay MB is not picked up during any of the three portions ofthe on period. For the second combination relay IPB is picked up becauserelay MB is picked up while relay MA remains down (rst portion) beforerelay PF has been picked up.

Relay ZPB is picked up for the third combination because relay MB is upwith relay MA down (third portion) after relay PF has been picked up.For the fourth combination relay MB is not up with relay MA down eitherbefore or after relay PF has been picked up. For the fifth combinationrelay IPB is picked up because relay MB is up while relay MA is down(rst portion) before relay PF has been picked up. For the sixthccmbination relays IPB and ZPB are both up because relay MB is up whilerelay MA is down both before and after (first and third portions) relayPF has been picked up.

In considering the organization of the line circuit illustrated in Fig.l, it will be understood that additional eld stations may be connectedbe- ,.tween the control oflice and the first station or between any twoof thev stations illustrated.

Control office equipment-The control oilice includes, besides theapparatus above mentioned, a quick acting line relay F of the polarbiased-toneutral type which has its contacts positioned to 'the rightwhen a (-i-) impulse is connected to the stepping line and to the leftwhen a impulse is applied to the stepping line from battery B. Relay Fis of the polar type for obtaining speed of operation only and it willbe obvious that a neutral type relay can be used if desired.

A quick acting line repeating relay FP of the neutral type repeats eachenergization of the line relay F, this relay being picked up each timethe line circuit is energized during a cycle of op` lerations anddropped between successive impulses.

Slow acting line repeating relay SA of the neutral type is energized atthe beginning of a cycle and because of its slow acting characteristics,it

remains picked up between successive impulses throughout the cycle andis dropped after a. predetermined time interval elapses following thelast impulse. SAP is provided for repeating the condition of the SArelay in such a manner that relay SAP is picked up at the beginning of acycle and dropped after a predetermined time interval elapses followingthe dropping of relay SA at the end of the cycle.

The impulses of a cycle cause the step-by-step operation of a steppingrelay bank including relays IV, IVP, 2V, 2VP and 3V. This stepping relaybank is arranged so that there will be a shift in position of some oneofA these relays for each deenergized condition of the stepping linecircuit as Well as for each energized condition of the stepping linecircuit. More specically, relay IVP is picked up during each odd offperiod and is dropped during each even olf period. Relay IV is picked upduring the conditioning and each even on period and is dropped duringeach odd on period.

Relay 2V is picked up during every second odd off period (first, fifth,ninth, etc.) and is dropped during alternate odd (third, seventh,eleventh, etc.) off periods. Relay EVP is picked up during every secondeven (second, sixth, tenth, etc.) off period and is dropped on alternateeven (fourth, eighth, twelfth, etc.) on periods. Relay 3V follows theoperation of relay 2VP in the same manner that relay 2V follows relayIVP. In other words, relays IV and IVP in combination are picked up anddropped once for each two im pulses in the line circuit and relays 2Vand 2VP in combination are picked up and dropped once for each twocomplete operations of relay IVP.

In this particular embodiment (because only four steps are illustrated)relay 3V is stuck up, when picked up, until the end of the cycle. Thisoperation of the stepping relay bank results in an exponential selectionof channel circuits, this feature being disclosed and claimed in theprior application of VV. T. Powell, Ser. No. 648,095 led December 20,1932.

Slow acting relays E and EP are for the purpose of timing the durationof the on periods. A starting relay STR is arranged to be picked up atthe start of each cycle and also to be dropped and picked up inaccordance with the position of relay EP to impulse the line. In otherwords, relay STR is a combined starting and line impulsing relay.

Ofhce control relay C is picked up at the start of a control cycle andremains up during such a cycle until the change to normal period at theend of the cycle. Relay C remains down during an indication cycle. Fieldcontrol relay FC is picked up at the start of an indication cycle.,

remains up throughout such a cycle and is dropped during the change tonormal period at the end of a cycle. Relay FC isnot picked up during acontrol cycle. Positive polarity control relay PC and negative polaritycontrol relay NC are used to selectively connect battery LB to the linecircuit during the olf periods, in preparation for energizing the linewith the proper polarity during the succeeding on periods.

Relay MA is connected in series with the A line return conductor andrelay MB is in series with the B line conductor. These two relays arefor the purpose of executing in the control office ,the conditions ofthe A and B lines during certain portions of the on period. While theserelays are indicated as being of the neutral type it is obvious thatthey may be ofthe polar type for An additional slow acting relay.

bus No. l.

.. MAB on indication bus.

Aprovided to be actuated subsequent to the proper positioning of thecontrol levers (not shown) for initiating the system for thetransmission of controls as set up by the levers.

A number of storing relays (not shown) for storing simultaneous ollicestart conditions interconnected with corresponding code determiningrelays such as relay CD, are so arranged that several storing relays maybe up at the same time but corresponding CD relays can only be picked uponeV at a time during successive operating cycles. The order in whichthe code determining relays are picked up is predetermined by theirrelative locations in the relay bank, all of which has been completelydisclosed in the prior application of N. D. Preston et al., Ser. No.455,304, led May 24, 1930, corresponding to Australian Patent 1501 of1931. This prior application likewise discloses the connections of theswitch machine and signal control levers, as well as the jumper con--nections which connect the contacts of relay CD to the PC and NC busesas illustrated by the dashed line ci Fig. 2.

For the purpose of illustrating station registration, a typical pilotrelay arrangement is fshown in Figs. 3 and 5. The pilot relays PO, PF,

IPB and ZPB are connected to the indication buses so that they may bepositioned on the first step of a cycle when indications aretransmitted. Relay PO (oil) is connected to ol indication Relay PF(operated by front contact of relay MA) is shown connected to the No. lMAF on indication bus. Relays IPB and 2PB (operated by back contact ofrelay MA) are connected through contacts of relay FF to the No. I Itwill be understood that the additional pilot relays may be provided andconnected to additional steps of the stepping relay bank, up to thepoint where sulcient codes for station registration are obtained.

Station relay 'IST is vprovided in Fig. 3 for the purpose oilregistering in the control oflice the station indicated in Fig. 4 whichit is assumed is transmitting indications. This station relay is merelytypical ci a number of such relays which would ordinarily be provided,one for registering each individual station. Additional relays similarto relay 1ST would be conne-cted to conductors indicated by referencecharacters IST, 2ST, 3ST, 5ST, 6ST, 8ST, 9ST, MST, HST and IZST whichare connected to the contacts ci relay ZPB as shown in Fig. 5.

Suitable indication storing relays, such as relays IR, `2IR and 31B, areprovided for storing thc various indications transmitted from the eld.1:stations, after a station has been registered in the control oihce bythe selection of a station relay. It will be understood that theserelays are merely typical of additional indication storing relays whichmay be provided for storing additional inff dications repeated byconditions at the field staupper left hand portion of Fig. 2. Relay D'isforthe purpose of delaying the connection to the upper winding of relaySIR..

Field station equipment-The eld stationvillustrated in Fig. 4 includes aquick acting re-l lay FI of the polar biased-to-neutral type, whichrelay is actuated to the right by positive current coming over the Sline from the control ofiice and to the left by negative current appliedto the S line in the control office. Relay FPI repeats the impulses inthe control line irrespective of their polarities.

Slow acting relay SA1 functions similarly to the corresponding relay SAin the control oiice, that is, it defines the bounds of each operatingcycle. It is picked up at the start of each cycle and dropped during thechange to normal period at the end of the cycle. Each field stationincludes a station relay SO1 which is picked'up at all stations at thestart of each operating cycle and after station selection only the SOrelay'associated with the selected station remains picked up. Lock-outrelay LO1 is picked up at the station which is sending indications overthe communication line, the circuits of this relay being so organizedthat when several iield stations have new indications to transmit atsubstantially the same time, the station nearest the end of the lineobtains connection withk ther communication system and other stationsare lockedV out.

Relay CHI at the eld station registers a change in the trailiccontrolling devices so that the sytem will be automatically startedthrough a cycle of operations for the transmission of new indicationswhenever relay CHI is down. Although the circuit of relay CHI is notshown in detail, it will be understood that it isnormally stuck up andis released to close its back contact |50 by the interruption of itsholding stick circuit, when a change in position of indication`repeating relays takes place. Relay CHI will register a change in one ormorel of a large number oi' devices and will initiate indication cyclesas long as there are new indications to be transmitted.

As above mentioned, the detailed circuits of these various relays havenot been included in the drawings of Fig. 4, since they are the same ashave been disclosed in other prior applications such as the abovementioned application of N. D. Preston, Ser. No. 644,481.

Relay PLAI conditions the A line conductor and relay PLBI conditions theB line conductor during the on periods and these two relays incombination form the six indication codes which are selectable duringeach "on period. Relay PLTI, in cooperation with relays PLAI and PLBI,controls the time space between each pair of impulses ior selectivelyconditioning the indication circuits to record a choice of twoindications (long or short oif) for each step taken by the steppingrelay bank.

Sequence determining relay SDI and sequence determining repeating relaySDPI function to deenergize the No. I sequence bus IS and to energizethe No. 2 sequence bus 2S in the order named. Relay SDI energizes the ISbus at the start of each on period anddeenergizes this bus about themiddle of each on period. Relay SDPI deenergizes the 2S bus atthe startof each on period and again energizes this bus a predetermined timeafter relay SDI deenergizes the IS bus during each on period. Theoperation of these'two sequence determining're-"IIS" aooaelie lays inenergizing these two buses in sequence, makes it possible to obtain thefour indication combinations numbered 3, 4, 5 and 6 of Fig 6. The nosequence bus NS, is supplied With permanent potential so that theconnection of an indication Wire to this bus results in relay PLB1 orrelay PLA1 being up through all three portions of a corresponding onperiod.

Suitable switch machine and signal relays (not shown) are provided ateach field station. The relays which repeat the condition of the switchmachine (WPl) and the detector track section (T1) are indicated but forthe sake of simplicity, the energizing circuits of these relays are notshown in the drawings.

It is believed that the nature of the invention, its advantages andcharacteristic features may be best understood by continuing thedescription in a manner relating to the detailed operation of thesystem.

Operation` While the system is in its at-rest or period of blankcondition, line S is deenergized. Lines A and B are energized by meansof a circuit which extends from the (-l-) terminal of battery LB, backcontact i8 of relay STR, back contact Il of relay SA, Winding of relayMA, A line conductor I2, back contact Ilil) of relay PLA1, back contacts||l| and |532 .of relays PLA2 and PLA3 respectively at other fieldstations (see Fig. l), resistance unit R1, conductor 236 (at laststation), resistance unit R2, back contacts |64, |65 and |06 of the PLBrel-ays (with suitable exponents) at all stations, B line conductor 3,Winding of relay MB, back contact I4 of relay SA and back contact l5 ofrelay STR to the terminal of battery LB. The current in this circuit iseiective to maintain relays MA and MB picked up when the system is inits normal condition.

Manual stcrt.-The operator initiates a cycle of operations for theselection of a particular iield station and the transmission of controlsto the selected station by positioning the necessary control levers (notshown) and then actuating starting button SB. The actuation of button SBWhile the system is normal causes the code determining relay CD to bepicked up. A circuit is now closed for picking up relay C which extendsfrom (-I-), back contact I 6 of relay SA, back contact Il of relay NC,front contact I8 of relay CD and winding of relay C, to Relay C closes astick circuit for itself extending from back contact i9 of relay SAP,front contact 20 and winding of relay C, to Relay C opens its backcontact 2| included in the circuit of relay FC, which prevents thepicking up of relay FC during this cycle.

A circuit is closed for picking up relay PC which extends from Jr) backcontact 3| of relay IVP, back contact 32 of relay 2V, back contact 33 ofrelay 3V, conductor 35, front contact 34 of relay C and Winding of relayPC, to A circuit is now closed for picking up relay STR which extendsfrom back contact 22 of relay SAP, front contact 23 of relay C andWinding of relay STR, to

The actuation of contacts l0 and |5 of relay STR opens the abovedescribed energizing circuit of the A and B line conductors and closes acircuit for energizing the S line conductor to mark the beginning of theconditioning on period. This circuit extends from the terminal ofbattery LB, front contact ID of relay STR, front contact 24 of relay PC,Vback contact 25 of relay NC, Winding of relay F, S line conductor 26,winding of relay F1 and over the above described circuit including the Aand B line conductors to front contacts 2l and 28 of relay STR. Thecircuit now continues through back contact 29 of relay NC, frontcontact30 of relay PC and front Contact l5 of relay STR, to the terminal yofbattery LB. i

Y Current `flowing in line S from the (-l-) termf contact 36 of relay Fin its right hand Idotted position and the Winding of relay FP, to RelayFP closes a circuit for picking up relay SA which extends from frontcontact 31 of relay FP and Winding of relay SA, to Relay 4SA maintainsits back contacts I I and |4 throughout the cycle so that the droppingof relay STR Will not be effective to connect battery LB to the A and Bline conductors.

It Will be understood that relays FP1 and SA1 at the iield station ofFig. 4 (as well as similar relays at other field stations) are picked upat substantially the same time as the corresponding relays in thecontrol oiice. Relay SA closes a circuit for picking up relay SAP whichextends from (-I-) front contact 38 of relay SA and Winding of relaySAP, to vRelay SAP opens its back Contact 22 Which causes the release ofrelay STR. The dropping of relay STR deenergizes the line conductors tomark the end of the conditioning on period and the beginning of thefirst ofi period. n

The picking up of relay SAP opens the above described stick circuit ofrelay C but this latter relay is not dropped, due to a substitute stickcircuit being closed at front contact I6 of relay SA before relay SAP ispicked up.

Relay S01 at the station is picked up during the conditioning period.Relay L01 is not picked up during this cycle and since its front contactis not closed, relay PLT1 cannot be energized. Since rel-ay L01maintains its front contact |66 open, the indication conditioningcircuits including conductors 202, 263 and 204 are not energized so thatrelays PLA1 and PLB1 remain down.

Line vimpulsing and stepping relay operation-,

The impulsing and stepping operations Will be d1- rected to Figs. 2 and3. Since relays F1 andFP1 at the eld station operate in synchronism withrelays- F and FP in the control oice, it Willbe obvious that thestepping relays |V1, |VP1, 2V1, 2VP1 and 3V1 Will operate in synchronismwith corresponding stepping relays in the control ofce when the circuitsare connected as shown in Figs. 2 and `3.

During the conditioning period, relay FPy is picked up as abovedescribed and closes a cirlay IVP is picked up to open its back contact4|.-

At the start of the rst off period (above described) the deenergizationof line Sdrops relays F and FP. Relay FP closes a circuit for picking uprelay |VP which extends from front contact 39 of relay SA, conductor|25, front contact 42 of relay IV, conductor |26, back conopen i.

, icA

tact 50 of relay FP, conductor |28 and winding of relays IVP, to RelayIV is stuck up after relay I VP picks up over a circuit extending from(-1-), front contact 39 of relay SA, back contact 4|] of Vrelay FP,conductor |21, front contact 5| and Winding ofk relay IV, to Relay 2V ispicked up at this time over a circuit extending from front contact 39 ofrelay SA, conductor |25, front contact 52 of relay IVP, back contact 53of relay 2VP, and Winding of relay 2V, to

The picking up of relay IVP opens the above described pick-up Ycircuitfor relay PC at back contact 3|'. Relay PC is immediately reenergized orrelay NC is energized, depending upon the connection of the No. Icontrol Wirev by Way of front contact 3| of relay IVP and front contact43 of relay 2V to the PC or NC bus as determined by the code jumperarrangement (not shown).

Relay E is now picked up over a circuit extending rom back contact 86 ofrelay 3V, front contact 44 of relay IVP, front contact 46 of relay IV,conductor |29 and winding of relay E, to Relay E closes a circuit at itsfront contact 41 for picking up relay EP. Relay STR is now picked up bymeans of a circuit extending from (-i-), front contact 48 oi relay SAP,front contact 49 of relay EP, front contact 23 of relay CV and Windingof relay STR, to The picking up of relay STR marks the end of the firstoff period and the beginning of the rst on period by again energizingthe line conductors.

The energization of line S results in relay FP picking up. Relay IV isnow dropped because one energizing circuit is open at back Contact 4| ofI VP and the other energizing circuit (through its front contact 5|) isopen at back contact 49 of relay FP. Relay IVP remains up during the onperiod over a stick circuit extending from front contact 39 of relay SA,front contact 49 of relay FP, conductor |26, front contact 4| andwinding of relay IVP, to

The dropping of rela-y IV opens the circuit of relay E at front contact46 and after a predetermined time interval relayV E drops, which iseffective to open the energizing circuit of relay EP at'contact 4'I andrelay EP drops after a predetermined time interval. The dropping ofrelay EP opens the above described circuit of relay STR at back contact49, so that relay STR drops to mark the end of the rst on period and thebeginning ofv the second off period by deenergizing the line Relay FP isnow dropped and relay IVP drops because both conductors |26 and |28 aredeenergi'zed at front contact 42 of relay IV and front contact 40 ofrelay FP, now in their deenergized positions. Relay 2V remains-energizedover a circuit extending from (-i-) on conductor |25, front contact 54of relay 2V, back contact 53 of relay 2VP and Winding of relay'2V, to

Relay 2VP'is now picked up by means of a circuit extending from (Jr) vonconductor |25, front contact 54 of relay 2V, back contact 55 of relayIVP and winding of relay 2VP, to

Relay 3V is now picked up over a circuit extending from on conductor|25, front contact 58 of relay 2VP and winding of relay 3V, to Relay 3Vcloses a. stick circuit for itself which is effective until the end ofthe cycle and which extends fromr on conductor |25, front contact |30and Winding of relay 3V, to

A circuit is now closed for picking up relay E which 'extends from(-1-), front contact 86 of relay 3V, back Contact |3| of relay IVP, backcontact 46 of relay IV, conductor |29 and winding of relay E, to Relay Eagain closes the above described pick-up circuit for relay EP afterwhich relay STR is picked up over its previously described pick-upcircuit. of the second oil period and the beginning of the second onperiod by energizing line S.

Relay FP now picks up and closes a circuit for picking up relay IV whichcircuit was previously described. Relay 2V remains stuck up after thepicking up of relay IV because relay IVP is down and a circuit iscompleted from on conductor |25, through back contact 52 of relay IVPand front Contact 56 oi relay 2V to thc winding of relay 2V.

The picking up of relay IV during the second on period as abovedescribed, results in relay E dropping because its circuit is open atback Contact 46 and because the circuit through iront contact 46 is openat iront contact 44 of relay IVP. Relays EP and STR now drop in turn todeenergize the line, which marks the end of the second on period and thebeginning of the third off period.

Relay FP again drops and by means of the previously described circuitwhen relay FP was dropped during the rst oll period, relay IVP is pickedup. Relays E, EP and STR now pick up in rotation, to mark the end of thethird oit period and the beginning of the third on period by energizingline S.

During the third oir period, relay 2V is dropped when relay IVP picks upbecause its circuit is open at back contact 53 oi relay 2VP and at backcontact 5.2 of relay IVP.

Relay FP again picks up and by means of the circuit described during thefirst on period, effects the release of relay IV. Relay E is now droppedsince its circuit is open at front contact 46 of relay IV and at backcontact ISE of relay IVP. Relays EP and STR now drop in rotation to markthe end or" the third on period and the beginning of the fourth oilperiod.

Relay FP now drops and causes the release of relay I VP in the samemanner as this relay was released during the second oir period. Relay2VP is now dropped because its stick circuit through its own frontcontact 53 is open at front contact 54 of relay 2V and at front contact52 of relay IVP. The pick-up circuit for relay 2VP through back contact55 of relay IVP is now open at front contact 54 of relay 2V.

Relay E is now picked up by means of a circuit extending from frontcontact 86 of relay 3V, back contact ISI of relay IVP, back contact 46civ relay IV, conductor |29 and winding oi relay E, to Relays EP and STRnow pick up in turn and the line circuit is energized to mark the end ofthe fourth off period and the beginning of the fourth on period.

Relay FP picks up and causes relay IV to be picked up by means of thecircuit described during the second on period. Relay E is now droppedsince the above described circuit through back contact 46 of relay IV isopen and the circuit through front contact 46 is open at front contact44 of relay IVP which is now down. Rclays EP and STR now drop and theline is deenergized to mark the end of theiourth "on period and thebeginning of the change to normal period.

Relay FP is dropped and relay IVP is picked up by means of the circuitdescribed during the rst off period. Relay E cannot be picked up at thistime because the circuit through front This marks the end contacts 46and 44 of relays IV and'IVP respectively is not completed to since relayl2VP is down which opens its front contact 45 and since relay 3V is upwhich opens its back contact 86. Since relay E cannot pick up, thecircuits are not closed for picking up relays EP and STR, which resultsin line S remaining deenergized lfor a time interval which is sufcientlylong to allow relay SA to drop, because its energizing circuit is openat front contact 3l of relay FP. Relay SA opens the circuit of relay SAPat front contact 38 and relay SAP is dropped.

The dropping of relay SA opens the stick circuit of relay C at frontcontact I5 before relay SAP drops and again closes this stick circuit atback contact I9, with the result Vthat relay C is dropped. Relays iV,IVP and 3V drop when relay SA releases and opens its iront contact 39.

From the above it will be seen that relay l VP is picked up during thefirst, third and change to normal off periods and dropped during thesecond, fourth and change to normal off periods. Likewise, relay IV ispicked up during the conditioning, second and fourth on periods and isdropped during the first and third on periods and the change to normalperiod.

It will be observed from a consideration of the above description and anexamination of the stepping relay circuits, that when relays IV and IVPare used in a larger system, they will be picked up and dropped in thesame order as shown in the present embodiment. In other words, relay IVPwill be picked up during each odd off period and dropped during eacheven ofi period, while relay IV will be picked up during theconditioning and each even on period and dropped during each odd onperiod.

It will also be observed that relays 2V and 2VP are controlled by twocontact sets (52 and 55) on relay IVP in the same manner that contactsets 40 and 50 of relay FP control relays IV and IVP. When the system isextended in size, additional relays such as relay 3V and relay SVP (notshown) will be controlled by'contact sets on relay 2VP which are similarto contact sets 52 and, 55 of relay lVP.

This results in relays 2V and 2VP countingr each pair of completeoperations o'f relay IVP and since relay IVP, in cooperation with relay`lV, counts each pair of relay operations of relay FP, it is apparentthat relay 2VP will count every four operations of relay FP or in otherwords, four complete orf and on periods. Therefore, four channelcircuits are selectable during four steps by the use of four steppingrelays. Relay 3V is only needed because of the additional channel(conditioning) shown in the present embodiment. By the addition o'f eachpair o stepping relays operating in the order above described, thenumber of channels selectable is doubled. This feature has beendisclosed in more detail in the above mentioned Powell application, Ser.No. 648,095.

Polarity selection of impulses-As above pointed out, when a cycle ofoperations is initiated manually from the control office, line Sis'energized with a (-1-) potential as determined by relay PC picking upby means of a circuit extending through back contacts 33, 32 and 3| ofrelays 3V, 2V and IVP respectively.

During the rst oil period after the conditioning period, the No. Icontrol is conditioned or by connecting through front Contact 3| o'frelay |VP and front contact 43 of relay 2V to the No. I control wire,which leads stepping relay bank by the through a front contact of theparticular CD relay which is picked up and the particular jumperconnection to either the PC or NC bus. During the second 01T period thiscircuit is switched from the No. I to the No. 2 control wire foractuating the PC or NC relay as determinedby the bus or leverconnection. During the third and foiuth off periods, the No. 3 and No. 4Wires respectively are similarly selected for determining the polaritywith which line S is to be energized following these olf periods. ItWill be noted that these control Wires are selected by Way of cont-actsof the stepping relays during the off periods, which donot shift duringthe succeeding on period so that the proper polarity is maintainedduring an on period as selected during the preceding oir period.

These control conditioning circuits Whichlead from contacts of relays 2Vand 3V through contacts o'f relay CD and the jumper and leverconnections to the PC and NC buses are not shown in detail, since theymay be similar to those disclosed in the prior application of N. D.Preston, Ser. No. 644,481.

The control executing circuits at the-eld station are likewise notshown, since these circuits may be controlled on the different steps ofthe (right hand dotted position) and the (left hand dotted position)actuations of relay F1, in a manner similar to that disclosed in theabove mentioned application, 644,481.

During afcontrol cycle, line S is energized during each on period inseries with the A and B lines in multiple, which results in picking uprelays MA and MB during these periods andfdropping them during the operiods. This is effective to pick up relay PF of Fig. 3 but as will belater pointed out, this condition in combination with a series ofnormally short off periods forms la phantom code, which results in nostation being registered in the controloflice.

Automatic start.'-The system may be initiated into a cycle of operationsfrom its normal position by an automatic change in condition at a eldstation. Such initiation may be the result of a change in traicconditions or it may be due to the operation of a traiiic controllingdevice to a new position, as a result of controls transmitted from thecontrol oflice. v

The stick circuit for change relay CH1 of Fig. 4 is interrupted whensuch a change in conditions takes place, so that this relay drops and-closes a circuit for picking up relay PLA1 which extends from backcontact |50 of relay CHl, backcontact |5| of relay FP1, back contact |52of relay SA1 and upper winding of relay PLAl, to Relay PLA1 closes astick circuit for itself extending from (-l-), back contact |53 of relaySA1, front contact |54 and upper Winding of relay PLAl, `to

Relay PLA1 opens the normally energized A and B line circuit at its backcontact |00, resulting in dropping relays MA and MB in the control oce.A circuit is now closed for picking up relay FC extending from backcontact 40 of relay SAP, back contact 59 of relay MB, back contact 2| ofrelay C vand winding of relay FC, to Relay FC closes a stick circuit foritself by way of its front contact 6|, which `is the same as the abovedescribed stick circuit VSTR which is the same as formerly traced, ex-

cept that it now extends through -Ir'ont contact 62 of relay FC insteadof front contact 23 of relay C. Relay STR energizes the S line cir-`cuit for marking theend of the normal period vand thebeginning of theconditioning period.

Relays F, FP, SA and SAP now pick up in turn i and the system is steppedthrough the cycle in theisame manner as previously described, except inthis case relays NC and PC are not selectively actuated to determine thepolarity applied to line S. Relay NC is maintained actuated by a circuitextending vfrom (-1-), back contact 63 of relay C and front contact 64of relay FC to the Winding of relay NC. Relay PC is not picked up duringthis cyclev because front contact S4 of relay C is not closed. Thiscircuit is effective to make all of the impulses applied to line Sduring this cycle in character.

InA the event that there are several stations withv indications totransmit at the same time atthe beginning of a cycle, the lock-outcircuit arrangement is eiective to permit the picking up of only onelock-out relay, for example, relay L01 of Fig. 4. Since this featureforms no part of the present invention and since it has been disclosedand explained in detail in the above mentioned prior application, Ser.No. 644,481, itwill not be shown or described in the present embodiment.It is sufficient for a clearunderstanding of the present invention toknow that relay L01 at only one i'ield station can be up at any onetime.

Transmission of indications- It will be assumed that the iield stationillustrated inFig. 4 is station No. 1 and that relay 1ST of Fig. 3 isthe station relay which is to be picked up to .register station No. l inthe control oice, when this station is transmitting. Ihis necessitatesthe connection of Wire 205 at the ield station by vmeans of jumper 200to (-1-), the connection of Wire 206 by jumper 20| to theNS busand thedisconnection of wire 201, all of which is indicated in Fig. 4.

Wire 205 connected to (-1-) by means of jumper 200 determines that therst 01T period will belong. When lock-out relay L01 is picked up duringthe conditioning period, a circuit is closed for picking up relay PLT1which extends from (-1-), front contact |56 o1" relay SA1, back contact-|51 of relay PLB1 in multiple with back Contact |58 of relay PLA1, frontcontact |55 of relay L01 and the winding of relay PLT1, to When relays|VP1 and 2V1 are picked up during the nrst off period, a circuit isclosed for picking up relays PLA1 and PLB1 which extends from (-1-),jumper 200, wire 205, front contact 59 of relay ZV1, front contact |60of relay I'VP1, conductor 202, front contact |G| of relay L01, backcontact |02 of relay FP1, front -contact |63 of relay PLT1 and the upperwinding of relay PLB1, to This circuit also extends through frontcontact |52 of relay SA1 and the upper winding of relay PLA1, to f rWithrelays PLA1 and PLB1 picked up, both back contacts |57 and |58 areopened, Whichresults in relay PLT1 dropping after a predetermined timeinterval. The drop-away time interval of relay PLT1 is considerablylonger than thepick-up time intervals of relays E, EP and STR andthedrop-away time of relay EPT in the control cnice. This results in thefailure vof relay STR to energize line'S for picking up relay FP toclose the stick circuit of relay EPT, -..(atfr ontY contact (il)v before`relay EPT drops ,after its pick-up circuit is opened-at back contact-65of, relay-EP.y `In other Words,.re1ay STR attempts to energize the Sline but fails, because both. return conductors |2 and |3 are open atback contacts and |06 of relays PLA1 and PLB1 respectively. Since boththe pick-up and stick circuits of relay EPT are open this relay isdropped.

During the succeeding (rst) on period, (started by the dropping ofrelays PLTl, PLA1 and PLB1) relays F and FP are picked up, and the No.off indication executing circuit is completed from (B+), back contact 68of relay EPT, front contact |59 of relay FP, front contact 'l0 of relayEP, conductor 7|, front Contact 'l2 of relay IVP, front contact T3 ofrelay 2V, No. ofi indication Wire 74 and lower Winding of relay PO, to(B Relay PO is picked up and stuck up by means of a circuit extendingfrom (-1-), front contact 75 of relay SA, conductor 16, front contact'il and upper winding of relay P0, to

Referring to the upper portion of the code table illustrated in Fig. 6,it will be noted that relay P0 is picked up when Wire 205 is connectedby jumper 200 to In the event that wire 205 is not connected to 4,-) (asillustrated for the No. choice oir indication), then relay PO remainsdown. This is brought about because the absence of an energizing circuitfor wire 205 results in relays PLA1 and PLB1 being down during the firstoil period, so that relay STR in picking up is effective to energizeline S to make this off interval short. This results in relay FP pickingup and closing the stick circuit of relay EPT at front contact 67 beforerelay EPT has time to release. In this case the No. ofi indicationexecuting circuit, as above described, extends from (B at front contact68 of relay EPT to the lower winding of relay PO and since this relayhas (B potential connected to the other terminal of the lower winding,it is not picked up.

By referring to Fig. 5, it will be observed that relay P0 is picked upto register stations 'l to I2 inclusive and this relay remains down toregister stations to 0 inclusive (excluding phantom No. d).

When the system advances from the first off into the first on period,line conductor S is energized, the return circuit being by way of the Aline conductor alone because relay PLB1 is picked up during the rst oirperiod to open line conductor E at back contact H05. The circuit iorpicking up relay PLBl extends from (-1-), NS bus, jumper 20|, wire 206,front contact |64 of relay ZV1, front contact |65 of relay |VP1,conductor 203, lower winding or" relay PLB1 and front Contact |66 ofrelay L01, to

With the A line conductor energized and the B line conductorde-energized, relay MA is picked up and relay MB remains down. Thiscondition continues throughout the rst on period because the abovedescribed circuit for picking up relay PLB1 is not interrupted andbecause there is no circuit established for picking up relay PLA1 duringthis period. With relay MB down there is no circuit completed forenergizing either wire8| or wire 93 (with B+) so that the juniper 20|being connected as shown in Fig. 6 for the No. on choice results inrelays PF, IPB and ZPB remaining down. l

Station registering relay 7ST is picked up when the system is advancedinto the second oli period by means of a circuit extending from (-1-),front contact 85 of relay 3V, conductor 98, front contact 81 of relayPO, back contact 88 of relay PF, back contact 89 of relay IPB, backcontact 90 of relay 2PB and winding of relay 1ST, to Since relay 3V doesnot drop until the end of the cycle, this circuit remains intact forholding relay 1ST up.

'The above example indicates how the particular station illustrated inFig. 4 is registered in the control cnice. It will now be explained howadditional combinations are obtainedso that ve other choices during thefirst step are effective to condition pilot relays PF, IPB and 2PB intheir up and down positions as indicated in the last column of Fig. 6.

The No. 2 choice is obtained when Wire 201 is connected to on the NS busby means of jumper 208 (see Fig. 6). This results in relay PLA1 being upand relay PLB1 being down throughout the first on period, so that the Bline conductor is energized and the A line conductor is de-energized.This causes relay MB to be picked up and relay MA to remain downthroughout this period, as indicated by reference letters U and Dassociated With these relays in Fig. 6.

With relay MB up and relay MA down, a circuit is closed for picking uprelay IPB which extends from (B+), front contact 18 of relay MB, frontcontact 80 of relay EP, front contact 92 of relay FP, back contact 19 ofrelay MA,` conductor 93, front contact 94 of relay IVP, front contact 95of relay 2V, No. I MAB on conductor 66, back contact 91 of relay PF andlower winding of relay IPB, to (B Relay IPB picks up and sticks by meansof a circuit through its front contact |61 to on conductor 16. nocircuits during this choice for picking up relays PF and 2PB. y

The No. 3 choice is obtained whenjumper 209 is connected to the IS busand jumper 2I0 is connected to the 2S bus as indicated in'Fig. 6. Thisresults in relay PLA1 being down and relay PLB1 being up during thefirst portion of the on period, relay PLA1 being down and relay PLB1being down during the second portion'of the on period and relay PLA1being up and relay PLB1 being down during the third portion of the onperiod. This is brought about by the sequence connection of Vpotentialto the IS and 2S buses. During the first off period, relay SD1 is pickedup by means of a circuit extending from ,front contact |80 of relay L01,front contact |60 of relay IV1, front contact |1| of relay Ii/'P1 andwinding of relay SD1, to Relay SDl closes a circuit by way of its frontcontact |12 for picking up relay SDP1.

Relay PLB1 is picked up during the rst portion of the iirst on period bya 'circuit extending from front contact |61 of relay SD1, ES bus, jumper209 (No. 3 choice, see Fig. 6), wire 206, front contact |64 of relay2V1, front contact |65 of relay IVP1, conductor 203, lower winding ofrelay PLB1 and front contact |66 oi relay L01, to Relay PLA1 remainsdown during this rst portion of the rst on period because the 2S bus iscie-energized at back contact |68 of relay SDP1, now picked up.

When relay |V1 drops during the first on period, the above describedcircuit of relay SD1 is opened at front Contact |90. Relay SD1 drops `tomark the end of the rst portion of the first on period and de-energizesthe IS bus, so that relay PLB1 is dropped during the second portion ofthe first on period. The 2S bus is deenergized during this secondportion because of the time interval before relay SDP1 drops to'energize this bus.

There arev The dropping of relay SDP1 marks the end of the secondportion of the on period andl energizes the 2S bus, so that a circuit isclosed for picking up relay PLA1 in the third portion, ex-

tending from back contact |68 of relay' SDP1, 2S busjumper 2I0 (see Fig.6), wire 201, iront contact |69 of relay 2V1, front contact |10 of relay|VP1, conductor 204, lower Winding of relay PLAl and front contactV |66of relay L01, to Relay'PLB1 remains down during the third portion of theon period because relay SD1 is down which de-energizes the IS bus. Thede-energization of the line to markl the end of the .on period also endsthe third portion of this period. 5

TlLis explains the up and down positions of relays PLA1 and PLB1 duringthe three on portions, as indicated by reference letters U andV Dassociated with the No. 3 choice in the table of Fig. 6. It will beobvious that relays MA and MB will assume opposite positions from relaysPLA1 and PLB1 because they drop when relays PLA1 and PLB1 pick up tode-energize the associated lines and they pick up When these relays atthe station drop to energize the lines.

When the No. 3 choice is executed, relays PF and 2PB are picked up andrelay IPB remains down. Relay PF is picked up because relays MA and MBare up during the second portion of the on period for closing a circuitfrom (B+), front contact I8 of relay MB, front contact 80 of relay EP,front contact 92 of relay FP, front contact 19 of relay MA, conductor8|, front contact 82 offrelay IVP, front Contact 83 of relay2V,conductor 84 and lower Winding of relay PF to Relay IPB can not bepicked up because this requires that relay MB be up and that relay `MAbe down before they are both up together and by referring to the tableofFig. 6 it will be noted that this condition does not exist. Relay MB ispicked up, however, while relay MA is `down during the third portion ofthe on period which is after relay PF has picked up. Therefore, acircuit is completed for picking up relay 2PB extending from (B+), frontcontact 18 of relay MB, front contact 60 of relay EP, front contact 92of relay FP, back contact 19 of relay MA, conductor 93, front contact 94of relay IVP, front contact 95of relay 2V, conductor 96, front contact91 of relay PF and lower winding of relay 2PB, to (B Relay 2PB sticks byway of its front con- 'tact |I2 and its upper winding to on conductor16.

The No. 4 choice is obtained when jumpers 209 and'2I0 connect wire 20Sto both the IS and 2S buses as indicated'in Fig. 6. This results inrelay SD1 connecting by way of the IS bus and wire 206 to thelowerwinding of relay PLB1 for picking up this relayduring the firstYportion of the on period. RelayPLA1 remains Vdown during this lportionof the on period because wire 201is not connectedto either bus.V Whenrelay SD1 drops to mark the end of the first portion ofthe on period,relay PLB1 drops because the I S bus is de-energized and relay PLA1remains down because wire 201 is open. Relay PLB1 is picked up whenrelay SDP1 drops to mark the end of the second portion of the on period,energizing the 2S bus by closing its back contact |68. Relay PLA1remains down during this portion of the on period because wire 201is`open.

The MA and MB relays will be inthe positions indicated opposite the No.4 choice, which positions-are as above explained opposite to the posi-[tionsofrelays PLA1 and PLB1.

vportion of the fon period and relayAPF is picked up as indicated. RelayPF sticks by energizing its upper Winding through its front contact I324to on conductor l5.V Since relay MB must ybe up with relay MA downbefore relay PF picks up for relay IPB to be pickedV up, it will beobserved that this condition does not exist so that relay `IPB remainsdown as indicated. Since relay MB mustpbe up and relay MA down afterrelay PFis picked up to energize relayZPB and since this condition doesnot exist for this choice, there is no. circuit for picking up relay 2PBand it Vremains down as indicated.

lThe YNo. 5 choice is effected by connecting wires 23'! and 265 to theIS and 2S buses respec# tively' by jumpers' ESQ and 2H). yThis resultsin relay PLAl being picked up during the first portion of the on periodbecause relay SD1 connects (-1-) to the IS bus at this time. Relay PLB1remains down during the rst portion of the "on period because the 2S busis de-energized at back Contact IES of relay SDPl. When `relay SD1`drops to advance the system into the second portion of the on.p`eriod,both the IS and 2S buses are de-energized so that relays PLA1 and PLB1are both down. When relay SDP1 drops to ad Vance the system into thethird portion of the fon period, the 2S bus alone isfenergized forenergizing Wire 208 and picking up relay PLB1. Relay PLA1 is down atthis time because Wire .20T connected to the IS bus is de-energized.

The MA and MB relays take opposite positions to the PLAl and PLB1 relaysrespectively' as indicated in the columns associated with these relays.Relay PF is picked up for this choice because relays MA and MB are uptogether (second portion), Relay 'lPB is picked up because relay MB is.up while relay MA is down before relay yPF picks up (first portion).Relay 2PB is down because relay MB is not up with relay MA down Yafterrelay PF is picked up (third portion).

The No. 6 choice is effected by connectingk jumpers 289 and 2li? fromWire 201 to both the IS and 2S buses. This results in energizing wire201 to piek up relay PLAl during the rst portion of the on period whenrelay SD1 is picked up. Relay PLB1 is down during all three portions ofthe on period because Wire 235 is left open. Relay PLA1 is down duringthe second portion of the on period because both the IS and 2S buses arede-energized after relay SD1 drops and before relay SDPl drops. RelayPLAl is picked up during the third portion of the on period because theES bus is energized for energizing Wire 207 when relay SDP1 drops.

As indicated in Fig. 6, relays MA and MB take positions opposite thePLA1 and PLB1 relays. This combination requires that relays PF, IPB and2PB all pick up. Relay iPB is picked up because relay MB is up withrelay MA down before relay PF is picked up (first portion). Rela'y PF isup because both the MA and MB relays are up at the same time (secondportion). Relay 2PB is up because relay MB is up and relay MA is downafter relay PF'is picked up (third portion).

' From the above explanation' and by referring to Fig. 6 it isseen Vthatthe first two choices of the six on indication combinations per step areobtained by selectively providing the return circuit for line S by Wayof line A and line B respectively.

Further, the additional four choices are obtained by the sequentialorder in which lines A and B are connected up to selectively provide thereturn circuit for line S.

More specifically, the third combinati-on is obtained by firstenergizing line A, next energizing line B, next de-energizing line A andthen deenergizing line B. The fourth combination is obtained by rstenergizing line A, next energizing line B, thenk cle-energizing line Band thereafter de-energizing line A. The fifth combination is obtainedby rstenergizing line B, next energizing line A, then de-energizing lineB and thereafter de-energizing line A. The sixth combination is obtainedby energizing line B first next energizing line A, then de-energizingline A and thereafter de-energizing line B.

Another Way of considering this feature of the invention is that lines Aand B are energized with combinations of three different lengths ofimpulses (long, medium and short) during a single impulse period of lineS. For example, choice No. d is a long impulse in line A, since relay MAis up during all three portions of the on period. No. 6 is a longimpulse in line B, since relay MB is up during all three portions of theon period. No. 5 is a medium impulse in both the A and B lines, sincerelays MA and MB are each up during only two portions of the fon period.No. 6 is a short impulse in line A because relay MA is only up duringone portion of the on period.,

, By referring to Fig. 5 and considering the different combinations inwhich the four pilot relays such a cycle because the off period betweenimpulses is normally short which causes relay PO to remain down. RelayPF is picked up and relays iPB and 2PB remain down during a cycle ofthis class, because relays PLA1 and PLB1 at the sta tion are down(because the lockout relay is down) resulting in relays MA and MB beingup in all three portions of the on period, which picks up relay PFbecause relays MA and MB are up together. Neither relay IPB nor relay2PB can pick up since there is no condition during the on period whenrelay MB is up with relay MA down .before or after relay PF is pickedup.

n the event that the number of stations required is more than ll, anadditional group of pilot relays similar to those shown in Fig. 5 isprovided, which results in obtaining M4 combinations for two steps ofthe stepping relay bank. Since one of these combinations is a phantomcode, the actual number of stations that can be registered in a systemusing two steps for station selection is 143. It` Will thus be seen thatthe number of combinations obtained equals twelve raised to the power ofthe number of steps used for station registration.

Indications from registered stations.-After a station is registered inthe control office by the actuation of its corresponding station relaysuch as relay 'EST of Fig. 3, the particular indications which are to betransmitted from the registered lthe right hand contacts III and |03 ofthese two station may be on a basis of'a choice of vtwo plus anadditional choice of three per step.

As an illustration of the manner in which this combination of choices istransmitted, the N o. 2 indication wires 2| I, 2|2 and 2|3 of Fig. 4Vare shown connected to contacts of relays T1 and WP1. Relay T1 is theusual track relay which repeats the occupied or unoccupied condition ofthe track section by being down and up respectively for these twoconditions. Relay WP1 is the customary relay which repeats the conditionof the track switch. For convenience, it is assumed that this relayactuates its polar contact 2|4 to the right and its neutral contact 2 |5to its picked up position when the associated track switch is in itsnormal locked position. When the track switch is in its reverse lockedposition, relay WP1 actuates its contact 2 I5 to its energized positionand its polar contact 2M to the left hand dotted position. When thetrack switch is unlocked, contact 2 I5 is dropped and contact 2 I4remains in its last actuated position.

Assuming that the track switch TS1 is unoccupied, relay T1 will bepicked up which removes potential from wire 2| I at theopen contact 2I6. Due to the absence of (-1-) potential on wire 2| I, the No. 2 oilindication is conditioned short in a manner which has already beenexplained in connection with the de-energized condition of wire 205during the rst step. This short off condition results in relay EPTremaining up for positioning indication receivingrelay IIR to thev leftover a circuit extendingfrom (B-) front contact 68 of relay EPT, frontcontact 69 of relay FP, front contact I of relay EP, conductors '1|,backcontact l2 oi relay IVP, front contact ||5 of relay 2V, No. 2 fofindication executing wire |I3, front contact I I 4 of relay 'IST andwinding of relay IIR, to (CN) Contact I I0 of relay IIR in its left handdotted position de-energizes the occupied conductor IE6, which mayconnect to an indicating device such as lamp OS for displaying theindication that the track section is unoccupied, by the `dark conditionof this lamp.

With relay T1 down due to the track section being occupied, wire 2| I isenergized resulting in a long off for dropping relay EPT, in the specicmanner already described in detail in connection with wire 205 duringthe rst step. With relay EPT down, (B+) is connected through backcontact 68 of this relay and over the remainder of the circuit abovedescribed to relay IIR, which is eiiective to position this relay to theright for energizing the occupied wire ||6 for displaying the occupiedcondition of the track section by lighting-lamp OS.

The above discussion relates to the choice of two distinctiveindications conditioned during the second oi period for execution duringthe second on period. It will. now be explained how an additional choiceof three indication conditions during the second on period may beobtained for execution during the same on period.

This choice of three may be conveniently used for registering the threerepeating positions of relay WP1, that is, normally locked, reverselocked and unlocked.

First assuming that relay WP1 is in its normally locked repeatingposition as indicated in Fig. 4, it is necessary -to position indicationreceiving relays 21R and 3IR to their right hand positions forenergizing the locked normal wire |08 by the'connection of (-1-)potential through 21R, to (CN). v is in such a direction that relay 21Ris positioned relays respectively.

During the second off period, a circuit is closed for picking up relayPLA1 which extends cause wire 2|2 is not energized. Since neither relay|VP1 or relay 2V1 shift during the second on period, this circuit iseffective throughout this on period to de-energize line A and energizeline B, resulting in relay MA remaining down and relay MB picking up.

With relay MB up and relay MA down, a circuit is closed for positioningrelays 21R and 3IR to the right, extending from (B+) front contact I8 ofrelay MB, front contact 80 of relay EP, front contact 92 of relay FP,back contact 'I9 of relay MA, conductor 93, back contact 94 of relayIVP, front Contact 99 of relay 2V, No. 2 MAB on indication executingwire |09, front contact 24 of relay IST and the lower windings of relaysZIR and 3IR in series to (CN).

f In the event that relay WP1 has its contact 2 I 5 in its energizedposition and its contact 2| 4 in its left hand dotted position, it isthen necessary to position relay 21R to the right and relay 3IR to theleft for energizing the locked reverse wire I I8 by means of an obviouscircuit.

With relay WP1 in this/assumed position, on the NS bus is extendedthrough front contact 2|5 of relay WP1, contact 2 |4of relay WP1 in` itsleft hand dotted position, conductor 2| 2, front contact |13 of relay2V1, back contact |65 of relay |VP1, conductor 203, lower winding ofrelay APLB1 and front contact |66 of relay L01, to This resultsr inrelay PLB1 picking up to `de-energize the B line conductor and sincethere is no circuit for picking up relay PLA1 under this condition, theA line conductor is energized.V This results in relay MA being picked upand relay MB being down.

A circuit is now closed from (B), back contact 18 of relay MB, frontcontact 80 of relay EP, front contact 92 of Vrelay FP, front contact 1Sof relay MA, conductor 8|, back contact 82 of relay IVP, front contact|I9 of relay 2V, conductor |20, front contact |2| of relay 1ST, windingof delay relay D and upper winding of relay The current flowing in thiscircuit to the right. Relay D is picked up and by means of its frontcontact |22 connects the upper winding of relay 3IR in multiple with theupper winding of relay 21R through contact |33 ofrelay 21R in its righthand position. Since the connection to this winding of relay 3IR isopposite from that of relay 21R, it is apparent that relay 3IR will bepositioned to the left for completing the above mentioned circuit forenergizing conductor IIB.

In the event that relay WP1 has its contact 2 I5 open due to theunlocked condition of the associated switch machine, then neitherconductors 2 |2 or 2|3 are energized for picking up the PLA1 or PLB1relays. This results in both the A and B line conductors being energizedthroughout the second on period for picking up relays MA and MB. Acircuit is now completed for positioning relay 21R to the left withoutdisturbing the condition of relay 3IR. This circuitextends from (B+)front contact 'l0 of relay MB, front contact before it is closedatcontact |22 of relay D.

With relay 21R positioned to theleit the circuit through contact ||l inits right hand position is interrupted so that neither wire E08 nor-WireH8 Will be energized. With contact |l| in its left .hand dotted positionthe unlocked wire |38 will be energized. It is obvious that these wires|88, H8 and |38 may connect to lamps or other indicating devices fordisplaying the proper indication. Or

wiresri and H8 may connect to indicating de- Ivices While Wire |38 maynot be used, which arrangement Will display an indication for either'locked condition and anV absenceof an indication for theunlockedfcondition.

, From the above examples, it is believed obvifous how the connections;cf the No. 3 and No. 4

indication wires of Fig. in different combinations can be used toexecute circuits comprisingv lthe No. 3 and No. d executing wires ofFig. 3.

These conditioningv and executing circuits-may be used for positioningadditional indication receiving relays associated with the registeredstation, or theyrmay oi course be used for 'registering a station in thecontrol once in the same manner as described in connection with, the No.conditioning and executing circuits if the system is of sufficient size.v l

End of indication cycle-The step-by-step operations and the impulsing ofthe S line circuit during an indication cycle are similar to thoseduring a control cycle, except for the length of the ofi periods whichhas been explained. After relays E and EP in the control cnice dropduring the last on period, they cannot be picked up during the next oirperiod (for the reason previcusly `explainedl Vso that relays F and FFin the control oilice and the corresponding relays at the eld stationremain down for a time interval Which is suciently long to drop relaysSA and SAP in the control office and the SA relay at the field station.The stoppinor relays are released in the same manner as described inconnection with a control cycle. Relay. FC of 2 drops when relay SAopens its front contact i6, which removes potential from Ythe stickcircuit of relay FC before relay SAP drops to apply potential to thisstick circuit. Relayv NC is dropped when relay FC drops and opensits-front Contact E4.

Lock-out relay L01 at the field station is ydeenergized in a mannerwhich., is not shown but which is completely disclosed in the 'abovementioned prior application, Ser. No. 544,481. The reason Yforyconnecting the pick-up circuit of relays PLT1 and SD1 through frontcontacts |55 and respectively of ,relay L01, is to prevent theunnecessary operation' of relays PLTI, SD1 and vSDP1 during vacontrol'cycle when relay L01 is down and the operation of theserequired. s

Lock-out between field stotz'ons.-It may happen that changes take placeat the several iield relays is not -stations simultaneously or in rapidsuccession so that more than one station may have indications totransmitrat the beginningof a cycle. In order torprevent lmore than onestation obtaining ac- .from the control oilice. Since this feature formsnoportion-of the present invention and since an example of the manner ofaccomplishing it is disclosed in the above mentioned Prestonapplication, Ser. No. 644,481, further discussion will be omitted.

Two-way transmissionr-It has been mentioned lthat control and-indicationcycles may occur separately or simultaneously. The operation for each ofthese cycles alone has been described and it will now be explained howthe system operates when controls and indications are transmitted duringthe same cycle. Such a cycle is conveniently referred to as a duplexcycle. It will be recalled that` relay C is up and relay FC is downduring a cycle for the transmission of controls alone. Relay C is downand relay FC is up during a cycle for the transmission of indicationsalone.

The actuation cfa starting button in the control oilice and the pickingup of relay CD which follows, results in picking up relay STR. whichmarks the beginning of the conditioning period. Relay FC cannot bepicked up after relay C picks up and opens its back contact 2|, butrelay FC can be picked up if there is a eld station waiting to transmitindications at the beginning of a cycle so that relay MB is downbeforerelay C picks up. Relay C can be picked up at the start of a cyclebefore relay NC is picked up during the conditioning period. Therefore,it is possible for both the C and FC relays 'to be up at the start of aparticular cycle of operations.

In this case, the continuous energizing circuit for relay NC isdisconnected at back contactv 63 of relay C andthe PC and NC buses areselectively conditioned in accordance with the jumper and leverpositions selected by the CD relay. This selective conditioning of thePC and NC relays is effective to provide the polar impulses forenergizing line S, to select the required eld station and to transmitcontrols to the selected station.

During a duplex cycle, a impulse is applied to line S during theconditioning period because relay PC is picked up over the previouslydescribed circuit through b ack contacts 33, 32 andV 3| of relays 3V, 2Vand |VP respectively. The following impulses applied to line S are l({)or (-'l as determined by the selective conzditioning oi the PC and NCbuses. circuit for line S is preconditioned by Way of the A and B linesand the lengths .of the off 'periods arepreconditimed, in the samemanner The return as has been described inV connection with theransmission of indications alone.

It is therefore evident that, since only Yone CD relay `in the control.cnice and one lock-out relay L01 at a eld station can be up at one timeduring a cycle of operations and since transmis- Asion yof controls andtransmission of indications are determined by separate and ydistinct,conditions of the line, these transmissions are independent of eachother and can be incorporated in the same operating cycle for obtainingthe The present embodiment has been described more' particularly withreference -to the character of the devices employed in a centralizedtraf- It will be understood that all possible combinations ofcircumstances cannot be consideredin detail and that the drawings anddescription have been limited as much as possible in order to avoidcomplicating the disclosure. Although one specific embodiment of thepresent invention has been shown, it is to be understood that variousrearrangements of the circuits may be made without departing from thespirit of the invention.

Having thus described one preferred embodiment of a centralized trafficcontrolling system, it is desired to be understood that the particulararrangements illustrated are only typical and are not intended toillustrate the' exact circuit design necessary to carry out the featuresof the invention, but have been selected to facilitate in the disclosurerather than uto limit its scope and it is further desired to beunderstood that various modifications, adaptations and'alterations maybe applied to the specific form disclosed in order to meet the problemsencountered in practice and that the system may be varied in the numberof eld stations to which the invention is applied and the amount ofapparatus included in a particular eld station, all without in anymanner departing from the spirit or scope of the present invention'except as limited by the appended claims.

What I claim is:-

l. In aremote control system, a stepping line circuit having a pluralityof series of time spaced impulses impressed thereon, a step-by-stepmechanism operable through a separate cycle for each of said series ofimpulses, means controlled by said mechanism for selecting three localchannel circuits for each step, means for causing said mechanism to takeone step for each time space between successive impulses of a series, arst return line and a second return line for said stepping line circuit,means for distinctively energizing two of said channel circuits inaccordance with the energized or deenergized condition of said returnlines for that step, and means for distinctively energizing the third ofsaid channel circuits in accordance with the length of the time Vspacefor that step.

2. In a remote control system, a stepping line circuit having aplurality of series of time spaced impulses impressed thereon, astep-by-step mechanism operable through a separate cycle for each ofsaid series of impulses, means controlled by said mechanism forselecting three local channel circuits for each step, means for causingsaid mechanism to take one step for each time space between successiveimpulses of a series, electro-responsive devices for eachlof saidchannel circuits, a iirst return linel and a second return line for saidstepping line circuit, means for distinctively energizing two of saidchannel circuits in accordance with the energized or deenergizedcondition of said return lines forrthat'step, means for distinctivelyenergizing the thirdof said channel circuits in accordance with thelength of the time space for that step, and means responsive to saiddistinct energization of the three channel circuits of each step forpositioning said electroresponsive devices in any one of six distinctivecombinations.

'3. In a remote control system, a stepping line circuit having aplurality of series of time spaced impulses impressed thereon, astep-by-step mechanism operable through a separate cycle for each ofsaid series of impulses, means controlled by said mechanism forselecting three local channel circuits for each step, means for causingsaid mechanism to take one stepfor each time space between successiveimpulses of a series', electroresponsive devices for said channelcircuits comprising a plurality of electro-responsivedevices for atleast one of said channel circuits, a rst return line and a secondreturn line for said stepping line circuit, means for distinctivelyenergizing tWo of said channel circuits in accordance with thesequential order of energization or deenergization of said return linesfor Vthat step, means for distinctively energizing the third of saidchannel circuits in accordance with the length of the time space forthat step, and means responsive to said distinct energization of thethree channel circuits of each step for positioning.

said electro-responsive devices in any oneof eight distinctivecombinations. 4. In a remote control system, a stepping line circuithaving a plurality of series of time spaced impulses impressed thereon,a step-by-step mechanism operable through aseparate cycle for each' ofsaid series of impulses, means controlled by said mechanism forselecting three local channel circuits for eachvstep,means for causing'said' mechanism to take one step for each time space between successiveimpulses of a series, a rst return line and a second return line forsaid stepping line circuit, means for distinctively energizing two ofsaid channel circuits for each step in accordance with the energized ordeenergi'zed condition of said return lines for that step, means forrecording the length of each time space between impulses, vmeans forstoring the recorded length of a time space during the succeedingimpulse, and means for distinctively energizing the third of saidchannel circuits in accordance with the stored length of said timespace.

5. In a remote control system, a stepping line circuit having aplurality of series of time spaced impulses impressed thereon, astep-by-step mechanism operable through a separate cycle for each ofsaid series of impulses, means controlled by said mechanism forselecting three local channel circuits for each step, means for causingsaid mechanism to take one step for each time space between successiveimpulses of a series,.a-rst return line and a second return line'forsaid step= ping line circuit, means for distinctively energizing two ofsaid channel circuits for each step in accordance with the sequentialorder of energization of said return lines for that step, means forrecording the length of each time space between impulses, means forstoring the recorded length of a time space during thesucceedingimpulse, and meansfor distinctively energizing vthe third ofsaid channel circuits'inaccordance ywith the stored length of said timespace. 1 Y

6. In a remote control system, a stepping line circuit having aplurality of series of time spaced impulses impressed thereon, astep-by-step mechanism operable through a separate cycle foreach of saidseries of impulses, means controlled by said mechanism for selectingthree local channel circuits for each step, means for causing saidmechanism to take one step for each time space between successiveimpulses of a series, arst return line and second return line for said,stepping line circuit, means for distinctively energizing two of saidchannel circuits for each step in accordance with the sequential Yorderof .deenergizaton of said return lines for that step, means forrecording the length of," each time space between impulses, means forstoring the recorded length QI a time space during the succeedingimpulse, and means for distinctively energizing the third ofsaidvvchannel circuits in accordance'with the stored length of said timespace.

7 Ina remote control system, a stepping line circuit havinga pluralityof series of time spaced impulses impressed thereon, a step-by-stepmechanism operable through aseparate cycle for each of said series ofimpulses, means controlled by said mechanism for selecting three localchannel circuits:r for each step, means for causing said mechanism totake one step for each time space between successive impulses of aseries, a rst return line and a second return line for said steppingline circuit, means for distinctively energizing two of said channelcircuits for each step in accordance with the sequential order ofenergization and deenergization of said return lines for thatstep, meansfor recording the length of each time space between impulses, means forstoring the recorded length of a time space during the succeedingimpulse, and means for distinctively energizing the' third lof saidchannel circuits in accordance with the vstored length of said timespace.

8; In a remote control system; a stepping line having a series of timespaced impulses impressed thereon; a plurality of return lines for saidstepping line; means for selectively energizing said rcturn lines incombination and in sequence for each impulse; means for selectivelyvarying the length of each time space between impulses; step-by-stepmechanism operated one step for each of said time spaces for preparing aplurality of channel circuits for each step; and means for energizingsaid channel `circuits for each step in accordance with the return lineor lines energized for that step, in

accordance with the sequence of energization of the return lines forthat step and in accordance with the length of the time space precedingthat step.

9-. In a remote control system; a stepping line having a series of timespaced impulses impressed thereon; a plurality of return lines for saidstepping line; means for selectively energizing said return lines incombination and in sequence for each impulse; means for selectivelyvaryingthe length of each time space between impulses; stepby-stepmechanism operated one step for each of Vsaid time spaces for preparinga plurality of channel circuits for each step; and means for energizingsaid channel circuits for each step in accordance with the return lineor lines energized for that step, in accordance with the sequence ofdeenergization of the return lines for that step andy in accordance withthe length of the time space preceding that step.

l0. In a remote control system, a rst line circuit ahd a second linecircuit, means for energizing and deenergizing said line circuits incombinations and `in sequential order, a selector mechanism controlledover said first line circuit, means controlled by said mechanism forselecting a plurality of channel circuits, a plurality of branches for afirst o'n'e of said channel circuits, means for distinctively energizinga second one of said chann'el cirillt's 'in accordance with theenergization 'r leenergizati'on Aof said line circuits, and means forenergizing said branches in accordance with the seduenti'al order ofenergization and deenergi'zatioh of said line circuits.

ll. In 'aremo'te control system, a rst line circuit ahd `a second linecircuit, means for energizing and deener'gizing said line circuits incombinatioiis an'd in sequential order, a selector mechni's'n'lcontrolled over said 'rst line circuit, means controlled by saidlmechanism for selecting a plurality ofl channel circuits, a plurality ofbranches for-a rst one of said vchannel circuits, means fordistinctively energizing a second one of said channel circuits inaccordance with the energization or deenergization of'said linecircuits, means respon-- sive to the distinctive energization of saidsecond channel circuit for selecting said branches, and means forenergizing said branches in accordance With the sequential order ofenergization and deenerg'izati'on 'of said line circuits.

' 12.v In ay centralized. traflic controlling system for railroads, acontrol oiice, a plurality of field stations,` a stepping lineconnecting saidoice with Said stations, a plurality of 'return linesconnecting said oflice with said stations, means only in said office forclosing and opening said stepping line to impress vtime spaced impulsesthereon, transmitting means at'each station for closing and opening saidreturn lines'V for distinctively conditioning 'said return lines foreach of said impulses. transmitting means at each station formaintaining said plurality of said return lines open after said oiiicecloses said stepping line for distinctively conditioning said steppingline and said return lines for each of said impulses, and lockout meansat one Kof said stations for preventing the operation of the associatedtransmitting means.

13. In a centralized traffic controlling system of the selector type,the combination with a control oice and a plurality of eld stations, asingle stepping line and a plurality of return lines connecting saidoil'lce with said stations, means for energizing said stepping line withfa plurality of impulses separated by normally short time spaces,selective mechanism fat said oilce and at said stations operated duringsaid time spaces in synchronism 'at said stations for selectivelyconnecting said return lines to said stepping line for energizing saidreturn lin in a plurality of combinations, means at said stations foropening said return lines to .provide abnormally long time spaces, arelay in series with each of said lines in the control cnice, and meansresponsive to the combinations of selective energization of said returnlines and the combinations of short and long time spaces in saidstepping lline for selectively operatingA said relays to register anyone of said stations in said oice during an operating cycle.

14. In a centralized tranic controlling system of the selector type, thecombination with 'a con-'- trol cnice Iand a plurality of eld stations,a single stepping line and a plurality of return lines connecting saidoffice with said stations, means for energizing said stepping line witha plurality of impulses separated by normally short time spaces,selective mechanism at said cnice and at said stations operated duringsaid time spaces in synchronism 4at said stations for selectivelyconnecting and disconnecting said return lines to said stepping line insequential order for energizing said return lines in a plurality 'ofcombinations, means at said station-s for opening said return lines toprovide abnormally long time spaces, and means respcnsive to thecombinations of selective energization of said return lines thesequential order of energization and deenergization 'of said returnlines and the combinations of short and long time spaces in saidstepping line for selectively operating said relays to register any oneof said stations in said office during an operating cycle.

15, In a selective type communication system; a central oiiice; a eldstation; a stepping line having in series therewith two return lines Inmultiple connecting said oflice and said station; means at said oflicefor applying to said stepping line a series of time spaced impulses;step-bystep means at said ofce and at said station caused to take onestep during each time space in said series; means at said stationeffective on each step to form a code in accordance with theenergization of only one, only the other or both of said return linesand in accordance with the order of energization When both areenergized; and means at said office distinctively controlled at eachstep in accordance with said code.

16. In a selective type communication system; a central oiice; a eldstation; a stepping line having in series therewith two return lin-es inmultiple connecting said office and said station; means at said officefor applying to said stepping line a series of time spaced impulses;step-bystep means at said office and at said station caused to take onestep during each time space in said series; means at said stationeiTective on each step to cause only one, only the other or both of saidreturn lines to be energized; means at said station effective on eachstep to cause said return lines to be sequentially energized in oneorder or the other when both are energized for that step and thereafterto cause one or the other 0I" said return lines to be deenergized forthe remainder of that step in accordance with a code; and means in saidofce distinctively responsive to the particular return line energized,the particular sequential order of energization of said return lines andthe particular sequential order of deenergization of said return linesprovided on that step.

17. In a selective type communicating system, a central ofce, a eldstation, a stepping line having in series therewith two return lines inmultiple connecting said oice and said station, an impulse relay at saidofIice, means including said impulse relay for applying to said steppingline a series of time spaced impulses, step-by-step means at saidstation caused to take one step during each time space in said series, afirst and a second stepping relay in said office, means for positioningsaid first stepping relay to alternate positions during consecutive timespaces, means for positioning said second stepping relay to alternatepositions during consecutive impulse periods, means controlled by saidstepping relays in combination for positioning said impulse relay toalternate positions during consecutive impulse periods and spaces, meansat said station effective on each step to form a code in accordance withthe sequential order of energizatio-n of said return lines, and means atsaid oflice selected by said first stepping relay and distinctivelycontrolled in accordance with said code.

18. In a selective type communication system;

a central office; a field station; a stepping line having in seriestherewith two return lines in multiple connecting said office and saidstation; means at said ofce for applying to said stepping line a seriesof time spaced impulses; step-by step means at said oiiice and at saidstation caused to take one step during each time space in said series;code forming means at said sta tion effective on each step to form acode in accordance with the order of energization of said return lines,comprising a rst bus permanently energized and second and third busesintermittently energized in a predetermined order; and means at saidofce distinctively controlled on each step in accordance with said code.

19. In a selective type communication'system; a central olce; a iieldstation; a stepping line having in series therewith two return lines inmultiple connecting said ofce and said station; means at said oflice forapplying to said stepping line a series of time spaced impulses;step-by-step means at said cnice and at said station caused to take onestep during each time space in said series; code forming means at saidstation effective on each step to form a code in accordance with theorder of energization of said re turn lines, comprising a first buspermanently energized and second and third buses intermittentlyenergized in a predetermined order; and decoding means at said oiiicecomprising a 'rst relay responsive to the simultaneous energization ofsaid return lines, a second relay responsive only when one of saidreturn lines is energized in advance of the other of said return linesand a third relay responsive only when said one of said return lines isdeenergized in advance of said other of said return lines.

20. In a centralized traflic controlling system for railroads, a controloiiice, a plurality of eld stations, a stepping line connecting saidoffice with said stations, a plurality of return lines connecting saidofce with said stations, means only in said oiiice for closing andopening said stepping line to impress time spaced impulses thereon, codeforming means at each station for energizing said return lines withcombinations of short and long impulses for each of said time spacedimpulses and code forming means at each station for maintaining saidplurality of return lines open after said oflice closes said steppingline for distinctively conditioning said stepping line and said returnlines for each of said impulses to thereby form codes, and meansresponsive to said codes for registering any one of said stations insaid cnice.

l WINFRED T. POWELL.

